In recent years, there has been proposed adoption of organic EL (Electro Luminescence) panels that rely on electroluminescence phenomenon of organic materials as display panels for display devices such as digital televisions. A matrix of respective organic EL elements of the R, G, and B colors is arranged in a substrate of an organic EL panel.
It is important to increase light-extraction efficiency of the respective organic EL elements of the R, G, and B colors, from the standpoint of reducing power consumption, increasing service life of the organic EL panels, and the like. To this end, there has been proposed a number of arts for increasing light-extraction efficiency owing to creativity of optical design of the organic EL elements (see Patent Literatures 1 to 7). For example, Patent Literature 7 discloses that respective light-emitting elements of the R, G, and B colors are each constituted from a lower electrode (mirror), a transparent conductive layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an upper electrode (half mirror) that are layered, and the optical distance between the mirror and the half mirror is adjusted in order to exhibit a local maximum of light-extraction efficiency of each of the R, G, and B colors (paragraph 0012). According to Patent Literature 7, the optical distance is adjusted by adjusting the film thickness of the transparent conductive layer for each of the R, G, and B colors (paragraph 0028).